Thermal mass flow meter GFM series

massfor gasportable

• rigid metallic construction • leak integrity 1 x 10-9 sccs of helium • NIST traceable certification • built-in tiltable LCD readout (some models) • circuit protection • can be used as a portable device • engineering units or 0 to 100% displays • totalizer option Description A low cost solution to thermal mass flow metering for gases is presented by Aalborg in introducing the model GFM mass flow meter line. The GFM design combines the convenience and accuracy of conventional mass flow devices with low costs previously unattainable. Each of these meters incorporate an advanced "U"-shape tube sensor in conjunction with flow passage elements constructed of aluminum and brass for non-corrosive gases or 316 stainless steel for corrosive applications. Principles of Operation Metered gases are divided into two laminar flow paths, one through the primary flow conduit, and the other through a capillary sensor tube. Both flow conduits are designed to ensure laminar flows and therefore the ratio of their flow rates is constant. Two precision temperature sensing windings on the sensor tube are heated, and when flow takes place, gas carries heat from the upstream to the downstream windings. The resultant temperature differential is proportional to the change in resistance of the sensor windings. A Wheatstone bridge design is used to monitor the temperature dependent resistance gradient on the sensor windings which is linearly proportional to the instantaneous rate of flow.